Hydraulic braking system



oct, 2s, 1941. B. sTLzr-:R Y 2,260,491

HYDRAULIC BRAKING SYSTEM Filed Nov. 10, 1939 2 Sheets-Sheet l q z5 $5/l0 56'/ 16 I 17 Y 6 9 25 r Il 28/ F' 29 i yl 1j Z9 INVENTOK oct.. 28,1941, B. STELZER l 2,260,491

HYDRAULIC BRAKING SYSTEM manual power is Patented Oct.-28, 1941HYDRAULIC BEARING SYSTEM Bertellisteuer, Dtroit, Mich. i ApplicationNovembei 10, 1939, Serial No. 303,837

4 Claims.

y The invention relates to hydraulic braking systems and moreparticularly a hydraulic brake booster in which a pressure boosteroperated by assisted by a power booster to augment the volume of uipumped to the wheel cylinders.' The present device is related to a brakebooster for which I filed an application for one end slides axial withsaid power piston' and extending' piece. Within saidpower cylinder 3moves a power piston or supplementary piston 5whose in the secondarycylinder 2. Co-

through it is a double-acting piston vIi consisting of a plunger orpiston of small displacement entering into said high-pressure Acylinder2, and a patent June 17, 1939, Serial No. 281,375,111 which a hydraulicpressure produced by manual power is stepped up by a source of power. f

The object of the present construction isto supply hydraulic fluid underhigh pressure to the hydraulic brake operating means, i. e., the wheelcylinders, b y manual power, and touse a power operated booster toincrease the volume of fluid supplied to the wheel cylinders, whichresults in a simplification of construction and consequent reduction ofthe cost of manufacturing.

Another object is to the excursions to a minimum with an accuracyinherent in the simplicity of construction, to eliminate the necessityof adjustment.

A further object is to provide a construction which is compact and has aminimum of external connections. y

Other objects and desirable particular conpisiganA I. A pistbn seal 1prevents escape from cylinder -2 either between the power piston 5 andcylinder of larger displacement sliding in cylinder 2 or the small endof piston 6. A similar piston v seal 1'Iseals the large end of piston 6,however,

. provide a followup valve which is novel in itself and which providesmaxi- Amum economy of power, and furthermore limits structions andarrangement of parts will become apparent upon reference to thefollowing detailed description of shown in the accompanying drawings, inwhich: Fig. 1 is a sectional elevation of thehydraulic brake boosterwith a diagrammatic illustration of the novel system; y

Fig. 2, a fragmentary sectional view ofthe follow-up valve when open to.admit power;

Fig. 3, a sectional elevation showing a modiflcation of Fig. 1, wherethe brake booster is constructed as a master cylinder;

Fig. 4, a fragmentary sectional view of the follow-up 'valve in Fig. 3when open to admit power;- and v Fig. 5, a side elevation illustrating amodified application, in'which brake pedal and accelerator y pedal arecombined.

Referring now vto the drawings for a more detailed description of mynovel braking system, there is illustrated in Fig. 1 a primary, `or lowpressure cylinder I, and a secondary, or high pressure cylinder 2, whichforms one piece with the power cylinder 3, closed by plate 4 extendingfrom cylinder I. The cylinders are co-axlally arrangedV and securedtogether to form one the two illustrativev embodimentsy then chamber I6may rigid tain` axial movement vis adaptedl to slide in the bore aconventional seal could be used here. A ceris possible between thedouble-acting piston B and power piston 5, however, it is limited to anecessary minimum by a stop, plate I8 secured to the power piston andretaining a follow-up valve consisting of a valve disc 9 sliding onpiston 6 and being pressed against a seat I by a spring II. Said seat I0is securely anchored at I2 (see Fig. 2) to'piston-6 and I3; a seal I4 isto prevent the passage o f air. An annular groove 15 in the power pistoncommunicates with low pressure chamber VIt of the power cylinder bymeans of -a passage I1. Air pressure is conducted tothe internal chamberI8 (see Fig. 2) of seat Il! through passage I9 and iiexible hoseconnection 20 from a source of air pressure 2 I, which may be theatmosphere when chamber IIiv is connected to a, source of vacuum, oritmay be an air pump, and chamber I6 then open to the atmosphere. Thus2| may designate an airl filter allowing air from the atmosphere, andthen `22 may designate a source of low pressureas avaouum pump or 'theintake. manifold of an internal combustion engine. When as a source ofpower air above atmospheric pressure is used, as in an air pump,

be open to the atmosphere and 22 may represent anair lter. The disc 9 oftheiollow-up valve is so dimensioned, that a small movement thereof isallowed between piston 5 and stop 8, whereby upon movement of said disc9 against stop 8, urged by spring 23, communication is establishedbetween low pressure chamber IB and chamber 24 of the power cylinderthrough passage I1, groove I5, and passage 25 in disc 9. A spring 26serves to; return the entire piston assembly to the trated in Fig. '1.In order to allowhydraulic fluid to pass from the primary cylinder tothe secondary cylinder when the resistance offered by the wheel.cylinders is small, I provide a ball check valve 21 allowing uid topass from-the primary oif position, .as illussage 29 in which `isloosely-placed a rod 29 to' crack the valve open when the pistons are inthe .oif" position so that the uid returned from theV wheel cylindersmay pass back to the master cylinder. A pin 30 prevents the ball fromfalling out.v Chamber 3| of cylinder 2 communicates through. thehydraulic' brake line 32 with the wheel cylinders 39, which areindicated diagrammatically. 'Ihe primary cylinder communicates with' themaster cylinder 3 If air pressure above atmospheric is .used as a\source of power, lcertain precautions must be taken to prevent-air toget into the 'hydraulic system. For this purpose I provide a seal 95 anda relief groove 36 open to the atmosphere through. passage 31 vandillter 38. Anotherrelief groove 39 inthe piston 6communicates withchamber I6.

Describing now the modiilcation shown in Figs.

and a `shell 42 forming'part-of the diaphragm power cylinder closed by acover 43 retaining a diaphragm 44 acting on a power piston 45 whichslidingly ts into said cylinder 40. The power piston 45v has an 'axial'bore in which slides Aa plunger. or control piston 46 entering intochamber 4| and operated by manual powerl through extension 41 connectedin some suitable manner to the conventional foot pedal 48. Betweenlshoulder 49 of control piston 46 and shoulder 50 i of extension 41slides a valve disc 5| against shoulder 49 by a conical disc spring 52,which while being' compressed flat, allows a small essed .movement ofdisc 5I against shoulder yor stop 56. An annular groove 53 communicateswith the low pressure chamber 54 connectingwith-a i source of. vacuum'as for instance the intake manifold 55 of aninternal combustion engine.

Chamber 56 communicates with chamber 54 through groove -53 and hole 51when vthe valve l disc is pressed away from thepowercylinder as shown inthe oi" .po-s i tjon1i'lig. 3, where the `l1valve disc' isfopened byspring 59. The sourceof. .pressure-which in the embodiment lshown by wayor example, is the atmosphere, communicat- *i'ngthrough air cleaner 59,hole 60, passage 6I;

end hole 62.with vchamber 63-is shut oil. in the "oif position, so rthatan equal. pressure exists `on both sidesv of the diaphragm. Chamber 56is sealed against atmospheric 'pressure by means of seal 64. Piston 45is sealed against piston 46 L and cylinder 49 by a seal 65 which sits ingroove 66 and slides in cylinder 40. Relative movement -3 and 4, thereis shown a housing consisting of i a hydraulic cylinder 40 having avchamber 4|` pressure builds up in-the `between lthe two pistons, ywhichis very small,

causes expansion and. contraction of the inner part of'cup .65, thusthis single seal is doing a dou duty, by sealingA piston 45 not onlyagainst the cylinder wall,` but also against piston 46.` To return thepiston-tothe oli position, as shown in Fig. 3, va returnspring 61 isprovided., 6,9 designates thehydraulic reservoir for the mastercylinder, where 69 is the\iluid level, 19

- .a small hole .which permits the hydraulic iiuid to return to thereservoir as well as'escapeof air from the system when the booster is inthe l o ipsition. Another passage 1| communicates .with chamber 12otthejpowerjpiston which is sealed againsttheatmosphere by a seal- 13.To-

complete the illustration `oi' the system I indicate a wheel cylinder 14in communication with chamber". i

the power .master cylinderor booster lis operated mechanically, it mustbe vmounted in some manner .to take lthe reaction.

For this purpose foot pedal 49.

v'I'his takes place Vtracted until disc 9,- contacts ,Seat III'chamber'.24 until piston 5 tionary member of In Fig. 5 the powermastercylinder of the construction shown in Fig."3 is mounted to the toe board11 of a motor vehicle, and the control piston 41 is operated by a footpedal 1l which e at the same time' serves-as accelerator pedal, 19representing the accelerator rod and 99 the In this embodiment thethrottle the toes and the brake with the the loss of time caused by theaccelerator pedal to throttle lever. is operated by heel, whicheliminates moving the foot from the brake pedal when applying thebrakes.

Considering now the device shown in Fig. l in operation, and assumingthat the'operator depresses the foot pedal which operates mastercylinder 34, a pressure cylinder, thus tending to force piston 6upwardly 23 and 26. As the pressurein chamber 2| is very low until thebrake shoes expanded by cylinders 33 touch the'brakedrums the hydraulicpressure does not build up in chamber 11, but merely passes throughpassage 28 past the check valve into chamber 3|l and from there to` thewheel cylinders, thus expanding the brake shoes.` with lthe booster atrest, the pistons being stationary. However, asthe shoes come intocontact with the drums, the hydraulic power piston 6 thereby tends tomove out of cylinder 2 but is prevented by some convenient stop on plate4. Piston 6 now moves upwardly by virtue of the'greater i'orce acting onthe lower end overpoweringthe force resisting the movement at theupperend which has a smaller displacement, assuming that the differenceis great enough to overpower/spring. 23, which is conthe power piston,closing groove I5. l At this point communication between chambers I6 and24 is interrupted. but still no power is `applied to thepower piston.piston 6 lcontinues tomove upwardly an additional resistance to thismovementis introduced by spring II whichnow also must be compressed;moves away from disc 9, as illustrated in Fig.` 2, thereby pressuresource of. pressure 2| through passage 25 into moves upwardlyin unisonwith piston 6, whereby` seat I'Il comes into contact withl disc 9 againwhen enough power has been applied.V vsupposing the 6, the valve disc ispushed away againfrom' the I5 and the lpressure is relieved It is lto bementioned that after check valve 21 closes, shutting oil' passage 29.

so While'the master cylinder 34 is applied 'the presber 11,\in thesameproportion as the displacesure vin chamber 3| -is greater than Aitisin cham-y ment of the primary en d of piston '6 is larger cylinder 49is :p ivotallyr secured at 15 to a sta- 75 ysidering the friction isnegligible.

chamber l3| depends on the ratio between vthe piston areas ofthecontrol' piston 6, i. e., bev

tween theprimary and secondary ends, the prothan that oi `the secondarycylinder.

upperl end which enters the This is not exactly so consures, however,the diiference due to the springs -ince the boosted pressure in portiongiven to piston 6 determines the vboosted pressure. v Piston 6really maybe considered as the carfasis pin-"16 of the is produced in line 16 andconsequently-in chamber 11 oi the primary entire system; the

is admitted from the l power is too great and.piston 5 moves faster thanpiston and that the pressure in the primary cylinder must be somewhatincreased to compress the springs. At higher. pres.

` up groove 53 'this position communication alone would not be sumcientto operate the wheel cylinders. For this reason the power pis-v ton isused to augment the volume of 4iiuid pumped from cylinder 2. Thepressure produced by the smaller endof piston 6 is maintained by theaction of the valve mechanism directing the power to the booster, whichcauses the power The power piston 5 piston to move with the controlpiston without increasing the hydraulic pressure in chamber 3|.Supposing that the source of power is not able to move piston 5 at therate piston 6 is moved, it is picked up by the latter through valve disc9, the Valve lseat in piston 5 serving as a stop, whereby the boosterratio is naturally decreased. When the operator releases the pressure onthe foot pedal so that it may return, .the pressure in chamber 11 isrelieved, whereby the pressure in chamber 3l acting on the small end ofthe control piston 6 pushes the latter downwardly towards the offposition. This results in immediate closing of the pressure line andopening of the passage between chamber-s I6 and 24, so that the entirepiston assembly, i. e., manually operated piston 6, and power operatedpiston 5, move downwardly into the off position, helped by spring 26.When the off position is reached again, valve 21 is cracked open by rod29, so that the fluid fromthe wheel cylinders is permitted to return viapassage 28 to the master cylinder.

The operation of the modiiied construction shown in Fig. 3 is similar inprinciple to that already described in Fig. 1. The difference is mainlylin the method of applying the control piston. Whereas in Fig. 1 it isdone hydraulically, in Fig. 3 it is performed mechanically. Furthermorethe power piston in Fig. 3 has to follow the control piston regardlessof the resistanceroiiered by the pressure in cylinder 4I.

Depression of foot pedal 48 causes piston 46 to enter into cylinder 4I,and -disc 5l to cover so that there is no communication between chambers56 and 54. The power piston 45 is pushed along by valve disc 5I andspring washer 52 with the control piston 46 by manual power. The seal 65passes orifice 10, and after the brake shoes come into contact apressure builds up in chamber 4l. As soon as said pressurel is greatenough to overcome spring 58, and assuming that the brake pedal isfurther depressed by the operator, spring 58 is further compressed, -andspring serves as a stop for the valve movement. In

is established between chambers 59 and 56 through passage 8|, so thatatmospheric pressure is admitted Yto the latter yto act on power piston.Thus the power piston and the control piston move in unison. When thecontrol piston is slowed down, or the power'admitted is somewhat greaterthan necessary, the control piston 46 will come into contact with thevalve disc 5I, so that the supply of power is shut oi, andl yet thepressure in chamber 56 is maintained. rThis might be called the holdingposition. When the operator takes his foot oi the brake pedal, wherebythe pressure in chamber 4I returns the control piston towards the offposition, away from the groove 53 so that the pressures the valve discis lifted in chambers 64 and 56 are immediately equalized and the powerpiston is also returned towards the off position by spring 61.

..1 wish it to be understood that byfuie term manual power used in thedescription I mean the control force'used by the operator eitherdirectly or indirectly. The most common means at the present is the footpedal, but a hand lever might'be used, or other more complicated controlmeans, which however boil down to direct application of manual force,application of manual force through somev intermediate means, and acontrol force indirectly released by the operator.

For the hydraulic brake operating means I have illustrated the wheelcylinders 33, but I do not wish' to be limited to these alone, as othermeans for applying brakes by fluid under pressure are also known or usedat present.

While three illustrative embodiments have been described in detail, itis not my intention to limit the scope of the invention to thoseparticular` embodiments or otherwise than by the terms of the appendedclaims.

l. In a hydraulic braking system fora vehicle havingv hydraulic brakeoperating means, a hydraulic master cylinder operated by manual power, acylinder, a small piston therein to supply a small volume of fluid underpressure to' Asaid brake operating means, means to operate said smallpiston by hydraulic manual power from said master cylinder, a powerpiston in said cylinder to supply an additional volume of fluid underpressure to said brake operating means, fluid transmitting means fromsaid cylinder to said brake operating means and to said master cylinder,a source of power to operate said power piston, a follow-up'valveresponsive to the movement of said pistons to admit power to the powerpiston to allow it to move in unison with the small one.

2. In a-hydraulic braking system for a vehicle having hydraulic brakeoperating means, a masterrcylinder, a pressure increasing device where apiston of a large displacement operates a piston of smallerdisplacement, said piston of a largel displacement. being adapted tomove in a cylinder which is in communication with said master cylinder,a secondary cylinder into which said piston of smaller displacement isadapted to move to produce a higher pressure, a power l piston adaptedto move into said secondary cyl- 52 is pressed flat, so that it inder,power means to force said power piston into said secondary cylinder,valve means responsive to the movement of the pistons actuated by thefluid from the master cylinder to apply said power means to move saidpower piston conlcurrentlyvwith the movement of said pistons actuated bythe uid from the master cylinder, a check valve 'to allow fluid-to flowfrom said master cylinder to said hydraulic brake operating means, andmeans to open said-valve when said pressure increasing device is inthefoil position, to allow the fluid to return to the `master cylinder.

3. In a hydraulic braking system for a vehicle having hydraulic b rakeoperating means, amaster cylinder, 'a brake booster consisting of aprimarycylinder in communication with said master cylinder, a secondarycylinder in communication with said hydraulic brake operating means,

a double-acting piston whose one end is adapted to slide in said primarycylinder and whose other and smaller end is arranged to enter into saidsecondary cylinder .to produce'a higher pressuf than exists in theprimary cylinder. a power piston surrounding the smaller end ofsaiddoubleacting piston and providing a1 sliding seal, said power pistonbeing adapted to slide in said sec ondary cylinder, a source oi' power,valve means l responsive to the relative position of said doubleactingpiston and said power piston to apply..

` -Yderu-a power piston adapted to enter into said boostercylinder, asmall plunger co-axial with said, power piston and adapted to slide inthe .latter to increase the pressure in said booster cylinder, saidplunger being operated by the hydraulic pressure from the mastercylinder. air pressure to` act on said power piston, meansto v limit therelative axial movement of the pistons said source of power to saidpowerfpiston so that' the latter moves in unison with said doubleiacting piston, to boost the volume of fluid transmitted to saidhydraulic brake operating means,

'and means to permit passage of iluid between and saidv saidhydraulicbrake operating means master cylinder? when the booster is in the "off"position.' a' y .4. In a hydraulic braking system having hydraulic brakeoperating means, a manually operated master cylinder. a hydraulicbooster cylin-

